PSI, Bar and kPa

Psi, bar and kPa are three units for measuring pressure. Tyre pressures are quoted in one or more of them, so the same pressure can look like three different numbers.

Last updated: 19 October 2026

What it means

Psi is pounds of force per square inch, bar is a metric unit, and kPa is kilopascals. NIST’s conversion tables give 1 bar as exactly 100 kPa, and 1 psi as 6.894 757 kPa, a figure the table does not mark as exact ^[1]. That makes 1 bar about 14.5 psi.

Why it matters when you buy

Your handbook, your gauge and your pump may not use the same unit. The Highway Code says tyres must be inflated to the vehicle manufacturer’s specification for the load being carried, so read the unit before you set a pressure ^[2].

A worked example

A handbook gives 2.2 bar. That is 220 kPa, and 220 ÷ 6.894757 is about 31.9 psi. A gauge reading of 32 psi is 32 × 6.894757, about 220.6 kPa, which is 2.21 bar.

Illustrative scenario: figures are examples, not quotes, valuations or market prices.

Related

• Tyre pressure converter
• Tyre pressure and tread depth: what the rules say
• Cold tyre pressure

Sources

1. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (pressure or stress), National Institute of Standards and Technology, nist.gov. The page shows no date. Checked 19 October 2026.
2. The Highway Code: Annex 6, Vehicle maintenance, safety and security, GOV.UK. Updated 22 October 2025, gov.uk. Checked 19 October 2026.